MicroRNAs (miRNA) are a recently discovered class of small non-coding RNAs (17-14 nucleotides). Due to their function as regulators of gene expression they play a critical role both in physiological and in pathological processes, such as cancer (Calin and Croce 2006; Esquela-Kerscher and Slack 2006; Zhang, Pan et al. 2007; Sassen, Miska et al. 2008).
There is increasing evidence that miRNAs are not only found in tissues but also in human blood both as free circulating nucleic acids and in mononuclear cells. A recent proof-of-principle study demonstrated miRNA expression pattern in pooled blood sera and pooled blood cells, both in healthy individuals and in cancer patients including patients with lung cancer (Chen, Ba et al. 2008). In addition, a remarkable stability of miRNAs in human sera was recently demonstrated (Chen, Ba et al. 2008; Gilad, Meiri et al. 2008). These findings make miRNA a potential tool for diagnostics for various types of diseases based on blood analysis.
Thus, although various markers have been proposed to indicate specific types of disorders such as Ovarian cancer there is still a need for more efficient and effective methods and compositions for the diagnosis of diseases.
Ovarian Cancer
Ovarian cancer is a cancerous growth arising from different parts of the ovary.
The most common form of ovarian cancer (≧80%) arises from the outer lining (epithelium) of the ovary. However, recent evidence shows cells that line the Fallopian tube (epithelium) also to be prone to develop into the same kind of cancer as seen in the ovaries. Since the ovaries and tubes are closely related to each other, it is hypothesized that these cells can mimic ovarian cancer. Other forms arise from the egg cells (germ cell tumor).
In 2004, in the United States, 25,580 new cases were diagnosed and 16,090 women died of ovarian cancer. The risk increases with age and decreases with pregnancy. Lifetime risk is about 1.6%, but women with affected first-relatives have a 5% risk. Women with a mutated BRCA1 or BRCA2 gene carry a risk between 25% and 60% depending on the specific mutation. Ovarian cancer is the fifth leading cause of death from cancer in women and the leading cause of death from gynecological cancer.
In early stages ovarian cancer is associated with abdominal distension
10-year relative survival ranges from 84.1% in stage 1A to 10.4% in stage IIIC
Ovarian cancer causes non-specific symptoms. Early diagnosis would result in better survival, on the assumption that stage I and II cancers progress to stage III and IV cancers (but this has not been proven). Most women with ovarian cancer report one or more symptoms such as abdominal pain or discomfort, an abdominal mass, bloating, back pain, urinary urgency, constipation, tiredness and a range of other non-specific symptoms, as well as more specific symptoms such as pelvic pain, abnormal vaginal bleeding or involuntary weight loss. There can be a build-up of fluid (ascites) in the abdominal cavity.
Diagnosis of ovarian cancer starts with a physical examination (including a pelvic examination), a blood test (for CA-125 and sometimes other markers), and transvaginal ultrasound. The diagnosis must be confirmed with surgery to inspect the abdominal cavity, take biopsies (tissue samples for microscopic analysis) and look for cancer cells in the abdominal fluid.
Treatment usually involves chemotherapy and surgery, and sometimes radiotherapy.
In most cases, the cause of ovarian cancer remains unknown. Older women, and in those who have a first or second degree relative with the disease, have an increased risk. Hereditary forms of ovarian cancer can be caused by mutations in specific genes (most notably BRCA1 and BRCA2, but also in genes for hereditary nonpolyposis colorectal cancer). Infertile women and those with a condition called endometriosis, those who have never been pregnant and those who use postmenopausal estrogen replacement therapy are at increased risk. Use of combined oral contraceptive pills is a protective factor. The risk is also lower in women who have had their uterine tubes blocked surgically (tubal ligation).
Ovarian cancer can also be a secondary cancer, the result of metastasis from a primary cancer elsewhere in the body. 7% of ovarian cancers are due to metastases while the rest are primary cancers. Common primary cancers are breast cancer and gastrointestinal cancer (A common mistake is to name all peritoneal metastases from any gastrointestinal cancer as Krukenberg cancer, but this is only the case if it originates from primary gastric cancer). Surface epithelial-stromal tumor can originate in the peritoneum (the lining of the abdominal cavity), in which case the ovarian cancer is secondary to primary peritoneal cancer, but treatment is basically the same as for primary surface epithelial-stromal tumor involving the peritoneum.
Staging
Ovarian cancer is staging is by the FIGO staging system and uses information obtained after surgery, which can include a total abdominal hysterectomy, removal of (usually) both ovaries and fallopian tubes, (usually) the omentum, and pelvic (peritomeal) washings for cytopathology. The AJCC stage is the same as the FIGO stage.                Stage I—limited to one or both ovaries                    IA—involves one ovary; capsule intact; no tumor on ovarian surface; no malignant cells in ascites or peritoneal washings            IB—involves both ovaries; capsule intact; no tumor on ovarian surface; negative washings            IC—tumor limited to ovaries with any of the following: capsule ruptured, tumor on ovarian surface, positive washings                        Stage II—pelvic extension or implants                    IIA—extension or implants onto uterus or fallopian tube; negative washings            IIB—extension or implants onto other pelvic structures; negative washings            IIC—pelvic extension or implants with positive peritoneal washings                        Stage III—microscopic peritoneal implants outside of the pelvis; or limited to the pelvis with extension to the small bowel or omentum                    IIIA—microscopic peritoneal metastases beyond pelvis            IIIB—macroscopic peritoneal metastases beyond pelvis less than 2 cm in size            IIIC—peritoneal metastases beyond pelvis >2 cm or lymph node metastases                        Stage IV—distant metastases to the liver or outside the peritoneal cavity        
Para-aortic lymph node metastases are considered regional lymph nodes (Stage IIIC).
Screening
Routine screening of the general population is not recommended by any professional society. This includes the U.S. Preventative Services Task Force, the American Cancer Society, the American College of Obstetricians and Gynecologists, and the National Comprehensive Cancer Network.
No trial has shown improved survival for women undergoing screening.
Screening tests include the CA-125 marker, transvaginal ultrasound, and combinations of markers such as OvaSure (LabCorp). A definitive diagnosis requires surgical excision of the ovaries and fallopian tubes, so a positive screening test must be followed up by surgery.
The purpose of screening is to discover ovarian cancer in early stages, when it is more curable, on the hypothesis that early-stage cancer develops into later-stage cancer. However, it is not known whether early stage ovarian cancer evolves to later stage cancer, or whether stage III (peritoneal cavity involvement) arises as a diffuse process.
The goal of ovarian cancer screening is to detect ovarian cancer at stage Several large studies are ongoing, but none have recommended screening In 2009, however, Menon et al. reported from the UKCTOCS that utilizing mutimodal screening, in essence first performing annual CA 125 testing, followed by ultrasound imaging on the secondary level, the positive predictive value was 35.1% for primary invasive epithelial ovarian and tubal carcinoma, making such screening feasible. However, it remains to be seen if such screening is effective to reduce mortality.